Use the full 0-127 resolution of a MIDI fader to control a smaller section of a parameter

To allow for more versatile parameter control MIDI learn should have the following options...

Slider for low value (defaults at minimum scale)

Slider for high value (defaults at full scale)

Using the default values MIDI learn behaves as normal, but if you would like to control only a small portion of a parameter in REAPER, lets say from -6dB to +6dB with the full throw of a MIDI fader you would set

Slider for low value = -6dB
Slider for high value = +6dB

Now when you move your MIDI fader from 0-127 the volume fader controlled goes smoothly from -6dB to +6dB!

Using a bit of thinking and inverted control of the Q setting (high value for the 'Slider for low value' and low value for 'Slider for high value') you can get the gain-Q interaction as in the video below...

Gain:
Slider for low value = 0
Slider for high value = +7.8dB

Q:
Slider for low value = 3.00
Slider for high value = 0.4

This kind of behaviour has already been implemented in other DAWs such as Ableton Live etc.